Electric motor rotor and a method for producing an electric motor rotor

ABSTRACT

A method of producing the core of an electric motor by providing a stack of laminations of magnetic material. Windows are formed in the laminations for one or more magnetic elements to be placed in each window. Each window has an end edge portion ( 17 ) which is to be at the peripheral edge ( 18 ) of the lamination of the finished version of the rotor. The laminations originally have an annular radial extension ( 60-61 ) and after the core is assembled with end caps, the annular radial extension ( 60-61 ) is removed so that the window end edge portions ( 17 ) are at the periphery ( 18 ) of the laminations. There is a polar peripheral portion ( 20 ) between each window and the periphery ( 18 ) of the lamination and an intermediate peripheral portion ( 40 ) between two adjacent polar peripheral portions, with such intermediate polar portions having reduced electrical conductibility and reduced magnetic permeability.

FIELD OF THE INVENTION

The present invention refers to a construction of a brushless electricmotor rotor and to a method for producing said rotor, carrying magnetelements which are internally circumferentially arranged and radiallyspaced from the lateral surface of the rotor.

BACKGROUND OF THE INVENTION

In he construction of a brushless electric motor rotor, the permanentmagnet elements are affixed to the core of said rotor to beconcentrically mounted around the motor shaft. In this construction, therotor is formed by longitudinally aligning a plurality of mutuallyoverlapped metallic laminations defining a lamination stack, eachmetallic lamination having a plurality of circumferentially alignedwindows which are angularly equidistant from each other and from themotor shaft, said windows being aligned to respective windows of theother metallic laminations of the lamination stack, in order to defineaxial housings into which the magnet elements are mounted and affixed.

In the prior art construction, each metallic lamination of the rotorlamination stack has a central portion provided with a central openingto be mounted to the motor shaft, and radially end portions, eachdefined externally to a respective window of the metallic lamination andincorporated to the central portion from the regions thereof locatedoutside two consecutive windows.

In his prior art construction, the windows of each rotor lamination aredefined so that the respective end edges are turned towards theperipheral edge of the respective rotor lamination, in a spaced positionfrom said peripheral edge of the lamination, in order to define thereina structural annular region connecting two adjacent radially endportions to each other and to the central portion of the laminationthrough the spacing existing between the adjacent end edges of twoconsecutive windows.

The existence of a structural annular region permits the use of metalliclaminations produced in a single piece and having windows which,posteriorly, with the formation o the rotor lamination stack, willdefine axial housings for the magnet elements.

While this known construction for a metallic lamination is adequate tobe manufactured on a large scale, relatively easer to carry out, of lowcost and which results in a highly reliable product, it has thedeficiency of permitting losses of useful magnetic flow to occur, whichfact is incompatible with the application to which the rotor isdesigned.

With this construction, only part of the total magnetic field of therotor generated by the magnets interacts with the magnetic field of thestator, whereas the remaining of said total field is lost in the form ofa dispersion field of both the rotor and the air gap. The rotor fieldlosses occur due to the presence of steel with a structural function inthe rotor lamination An the magnet end region. This region serves as apathway to the flow lines of the dispersion field, which represent anon-used amount of the total field of the rotor.

DISCLOSURE OF THE INVENTION

Thus, it is an objective of the present invention to provide an electricmotor rotor and a method for producing an electric motor rotor, whicheliminates the magnetic flow losses due to the rotor dispersion field,has high energetic efficiency and high reliability, and which may beobtained with an easy, economical and industrially viable construction,without impairing the integrity and strength of the rotor.

These and other objectives are achieved by an electric motor rotor,comprising: a core, formed by a plurality of metallic laminations, whichare axially and mutually overlapped and which are made from a magneticmaterial; polar peripheral portions in a magnetic material and affixedaround the core; and an equal number of magnet elements, retainedbetween the polar peripheral portions and the core, said rotorcomprising a cylindrical lateral surface defined by the polar peripheralportions, which are circumferentially spaced from each other, and byintermediate peripheral portions provided between each two adjacentpolar peripheral portions, said intermediate peripheral portions havingthroughout their longitudinal extensions reduced electricalconductibility and reduced magnetic permeability in relation to thecore, at least in the regions connecting two adjacent polar peripheralportions, said rotor further comprising a pair of end caps for retainingthe polar peripheral portions to the core. The present invention furthercomprises a method for producing an electric motor rotor of the typementioned above, comprising the following steps: a providing eachmetallic lamination with a plurality; of windows, each window having endedges turned towards a peripheral edge of the respective metalliclamination, with the end edges of all the windows being contained in thesame circumference; b- providing each metallic lamination, from itsperipheral edge and at least in the regions radially aligned with theadjacent end edges of each two consecutive windows, with a respectiveradial extension, which is coplanar and external to said peripheraledge; c- overlapping the metallic laminations, defining over an end capa lamination stack, so that each window of said laminations be axiallyaligned with respective windows of the other metallic laminations,defining, with the end cap, axial housings along the rotor; d- insertingan adhesive material into the axial housings; e- inserting into eachaxial housing a magnet element: f- mounting and affixing another end capto the lamination stack, already retaining each magnet element to therespective axial housing: q- curing the adhesive material, retainingeach magnet element to the respective axial housing; and h- removingeach said radial extension, so that the peripheral edge of the metalliclaminations defines the transversal contour of the finished rotor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below, with reference to the attacheddrawings, in which:

FIG. 1 illustrates, schematically, a cross-sectional view of the rotormounted with a metallic lamination of the rotor lamination stack,constructed according to the prior art;

FIG. 2 shows, schematically, a cross-sectional view of the rotor mountedwith a metallic lamination of the rotor lamination stack, constructedaccording to a first embodiment of the present invention and in anon-finished rotor condition;

FIG. 3 shows, schematically, a cross-sectional view of the rotor mountedwith a metallic lamination of the rotor lamination stack, constructedaccording to a second embodiment of the present invention and in anon-finished rotor condition;

FIG. 4 shows, schematically, an enlarged cross-sectional view of thealready finished rotor;

FIG. 5 shows, schematically and in longitudinal view according to lineV—V of FIG. 4, an already finished rotor, obtained according to one ofthe first and second embodiments of the present invention;

FIG. 6 shows, schematically and in longitudinal view according to lineV—V of FIG. 4, an already finished rotor, obtained according so anotherembodiment of the present invention; and

FIG. 7 shows, schematically and partially, an enlarged plan view of partof the metallic lamination illustrated in FIG. 2 and shown as det. a.

BEST MODE OF CARRYING OUT THE INVENTION

According to the figures, the electric motor rotor of the presentinvention comprises a core 10, defined by a plurality of metalliclaminations 11 in a magnetic material, such as steel, which have adetermined electrical conductibility and a determined magneticpermeability, and which are mutually concentric and overlapped, forminga lamination stack to be affixed around an extension of the shaft S ofthe motor, and polar peripheral portions 20 affixed around the core 10.Between each said polar peripheral portion 20 and the core 10 is definedan axial housing 12, which occupies the whole longitudinal extension ofthe rotor and into which is retained a respective magnet element 30,said magnets being usually in the form of longitudinal plates, which arefor example arcuated (or rectilinear) and which are placed according toa same circumferential alignment and spaced from each other.

According to the prior art, each metallic lamination 11 has a centralportion 13 provided with a central opening 14 to be mounted to the shaftS of the motor, windows 15, which are defined according to the samecircumferential alignment and which are angularly equidistant from eachother and from the shaft S of the motor, and radially end portions 16,each defined externally to a respective window 15 and incorporated tothe central portion 13 by the regions thereof between each two adjacentwindows 15.

The windows 15 of each rotor lamination have respective end edges 17circumferentially contained in the same circumference and facing aperipheral edge 18 of the respective metallic lamination 11 whichdefines the contour of the cross-section of the finished rotor.

The overlapping of the metallic laminations 11, in order to form thelamination stack, is carried out so is that the windows 15 of eachmetallic lamination 11 be aligned with the respective windows 15 of theother metallic laminations 11 of the lamination stack, defining theaxial housings 12 to allow the assembly and fixation of the magnetelements 30. Upon formation of the lamination stack, each axialalignment of the radially end portions 16 defines a respective polarperipheral portion 20.

The magnet elements 30 are retained to the core 10 by an interface of aretaining adhesive material, for example a curable polymeric material,which fills in the gaps existing between each magnet element 30 and therespective axial housing 12. The adhesive material has low electricalconductibility and also low magnetic permeability, in relation to thesame characteristics of electrical conductibility and magneticpermeability of the core.

According to the illustration in FIG. 1, the prior art construction hasthe end edges 17 of the windows 15 of each metallic lamination 11contained in a circumferential alignment internally defined in relationto that alignment containing the peripheral edge 18 of the metalliclamination 11 in a position spaced from said peripheral edge 18, inorder to define therein a structural annular region 19 connecting twoadjacent radially end portions 16 of each metallic lamination 11 to eachother and to the central portion 13 thereof by the spacing existingbetween the adjacent end edges of two consecutive windows 15. In thisconstruction, the lamination stack defines the rotor cylindrical lateralsurface, which is metallic throughout its axial extension. Thestructural annular region 19 provides a structural connection, which issufficient to resist the centrifugal forces on the magnet mass and onthe mass of the steel material existing on the magnets, but whichpermits the occurrence, in this region, of magnetic flow lines whichresult in the losses due to dispersion field discussed above.

In order to solve the problems of magnetic flow losses due to thedispersion field existing in the prior art, the rotor of the presentinvention is constructed in such a way that, when finished, thelaminations of its lamination stack have no more the respectivestructural annular region 19 connecting each two end regions 16. Thisrotor has, at least in this finished condition, a cylindrical lateralsurface with metallic regions, which are circumferentially intercalatedby regions comprising, throughout its longitudinal extension, reducedelectrical conductibility and reduced magnetic permeability, as comparedto the steel which forms the core.

According to the present invention, the cylindrical lateral surface ofthe rotor is defined so that each two polar peripheral portions 20 becircumferentially intercalated by an intermediate peripheral portion 40having, at least in the regions connecting two adjacent peripheralportions 20, reduced electrical conductibility and reduced magneticpermeability in relation to the core 10. The intermediate peripheralportions 40 comprise end regions 41, which connect the adjacent polarperipheral portions 20, and a median region 42.

According to the present invention, each end region 41 of anintermediate peripheral portion 40 is defined by the circumferentialspacing between the respective median region 42 and the adjacent polarperipheral portions 20, said median region 42 being defined, forinstance, by a respective peripheral portion of the core 10circumferentially spaced from the adjacent polar peripheral portions 20,each end region 41 being defined by the end of an axial housing 12 of amagnet element 30 filled in with the adhesive material for retainingsaid magnet elements 30 (FIG. 4). This adhesive material is a retainingagglomerating means, such as resin, rubber, etc., which involves themagnet elements, avoiding the eventual release of chips therefrom, andwhich provides finish to the lateral surface of the finished rotor atthe end region 41.

For producing the rotor of the present invention, the lamination stackis formed by seating a first metallic lamination 11 of this laminationstack onto an end cap 50 of a pair of end caps 50 which form the rotor.This seating preferably occurs by resin being applied onto an upper faceof the end cap 50 located under the lamination stack of the rotor. Theend caps 50 are obtained from a material with non-magneticcharacteristics, in order to eliminate or minimize, in said caps, themagnetic field due to dispersion and passing through said caps and theconsequent losses. According to a constructive form of the presentinvention, as illustrated in FIGS. 2, 3 and 5, the finished rotorcomprising a core 10 and polar peripheral portions 20 is produced with astack of stamped metallic laminations 11 incorporating from theperipheral edge 18 thereof, at least in the regions which are radiallyaligned with the adjacent end edges 17 of each two consecutive windows15, a radial extension 60, which is coplanar and external to saidperipheral edge 18 and which is inscribed in a circumference which isconcentric and external in relation to that containing said end edges 17which, in the present embodiment, surpass radially the peripheral edge18 of the respective rotor lamination in the region of the correspondingradial extension 60. The radial extensions 60 may have any shape. In theembodiment in which the metallic lamination 11 is square, said regionsare defined by the vertex portions of said laminations. The dimensioningof the metallic laminations 11 is determined so that said laminationsare shaped having the internal diameter of the stator, as it occurs withthe metallic lamination illustrated in FIG. 2, or in such a way as touse a smaller quantity of raw material in the stamping process thereof.In this case, the metallic lamination 11 has its shape limited by apolygon, for example a square, whose sides are tangent to the excessmaterial external to the peripheral edge 18.

According to the illustrations of FIGS. 2 and 3, each rotor laminationis shaped so as to have a single radial extension 60, which is annularand continuous and which determines a rotor lamination with a largerdiameter than the nominal diameter of the already finished rotor.

The thickness of each radial extension 60 is calculated to guaranteeintegrity to the metallic laminations 11 during their manufacture andformation of the lamination stack and during rotor machining, withoutcausing high losses in the material which forms the laminations.

In a constructive option illustrated in FIG. 3, the single radialextension 60 incorporates in each region radially aligned with theadjacent end edges 17 of each two consecutive windows 15, an additionalreinforcement portion 61, which is radial, coplanar and external inrelation to said single radial extension 60.

According to another form of carrying out the present invention,illustrated in FIG. 6, the core 10 is produced bad a lamination stack,each metallic lamination 11 being stamped so as to have the respectiveperipheral edge 18 shaped to define a radially internal edge of arespective axial housing 12 for a magnet element 30. In this embodiment,the radially external edge of each said axial housing 12 is defined bythe radially internal edge of a respective polar peripheral portion 20,which is radially mounted spaced from the core 10, after the formationof the latter, in order to. define, in this spacing, an axial housing 12to be filled with the adhesive material for retaining the respectivemagnet element 30.

According to this embodiment, after the formation of the rotorlamination stack, adjacently and spaced from each portion of theperipheral edge of this stack, is mounted a respective polar peripheralportion 20, in the form of a massive shoe or consisting of superposedlaminations, which are attached to each other, for example, by gluing,riveting, bolting, etc. In this embodiment, the shoes are individuallymounted and affixed to the rotor by retaining elements 21 (bolts,rivets, gluing between each support and the caps, etc., positioned in aplace which minimizes the losses caused by hysteresis and Foucaultcurrent), extending longitudinally through the respective polarperipheral portion 20 to a pair of end caps 50, each cap being mountedadjacently to a metallic lamination 11 provided at one of the ends ofthe lamination stack. In order to form each axial housing 12 providedwith shoes, it is necessary to use a mold or a device to determine theshape of the end walls of each said housing, so as to retain theadhesive material for affixing said magnet elements 30 in thesehousings. According to the rotor embodiment illustrated in FIGS. 2-5, inorder to form the rotor lamination stack, after superposing the metalliclaminations 11 (and eventually gluing one to the other, which minimizeslosses due to hysteresis and Foucault current) over an end cap 50provided under the lamination stack, thus forming the core 10, eachaxial housing 12 defined by the longitudinal alignment of the windows 15of the metallic laminations 11 of the lamination stack receives theadhesive material for affixing the magnet elements 30, before placingthe latter in said axial housings 12.

In this construction, after affixing the other end cap 50 and achievingthe cure of the adhesive material for retaining the magnet elements 30,the rotor is submitted to a process for removing the excess of materialwhich forms the metallic laminations 11, for example by machining, untiltheir end edges 17 are contained in a circumference with a diameter atminimum equal to that of the circumference circumscribing the finishedrotor. Machining of the lamination stack is carried out until thedesired final diameter of the rotor is obtained, defining theconfiguration illustrated in FIG. 4 with the core 10 and polarperipheral portions 20.

The attachment of the caps to the rotor lamination stack and to eachother may be obtained by retaining elements 21. such as rivets, bolts,etc. By machining the lamination stack, the end edges 17 of the windows15 of the metallic laminations 11 Which form said lamination stack areopened to the transversal contour of the rotor and defined in theseregions by the cured adhesive material which fills the axial housings12.

With this construction, each machined lamination of the rotor laminationstack has its end radial portions 12 defined externally to an adjacentmagnet element 30 and retained to the central portion 13 by the adhesivematerial which fills each axial housing 12.

The Provision of one or more radial regions 60 from the peripheral edge18 of each rotor lamination coinciding with the circumference whichdetermines the desired final diameter of the rotor assures the metalliclaminations 11 to have mechanical rigidity during their manufacture andallows them to be industrially produced on a large scale.

Since the radial extension 60 of the metallic lamination illustrated inFIG. 2 is small, said metallic lamination may be stamped simultaneouslywith the lamination of the stator, which reduces the production time andminimizes material losses when removing excesses.

The solution of a metallic lamination having a reinforcement additionalportion 61 illustrated in FIG. 3 has the advantage of having strength,requiring less precision as regards tooling and production process.

In a form of producing the rotor configuration illustrated in FIG. 6,after producing the lamination stack which defines the core 10, thepolar peripheral portions 20 are placed and maintained, by appropriatemeans, radially spaced from the core 10, on the end cap 50 providedunder the lamination stack, defining in this spacing an axial housing 12to be filled with the adhesive material for retaining the magnetelements 30. After this filling has been completed, each axial housing12 receives a magnet element 30, before the other end cap 50 and theretaining elements are provided, closing the assembly. with thisconstruction, the produced rotor does not require posterior machining,since its diameter may be defined during the relative positioningbetween the polar peripheral portions 20 and the core 10 for receivingthe magnet elements 30.

The adhesive material used between the end caps 50 and the rotorlamination stack may be also provided between the metallic laminationsof the lamination stack and has the Function of filling in the gapsbetween the magnets and the edges of the housings for the magnetelements defined in the rotor; structurally retaining the magnetelements 30 to said housings, compensating the centrifugal androtational forces to which said magnet elements 30 are submitted;reducing, by a dampening effect or by deformation of the layer ofadhesive material, the high thermal stresses (associated to temperaturevariation of the rotor and to the different coefficient of dilatation ofthe materials which are interconnected by the adhesive material) Whichare generated in the magnet elements 30 and which are usuallydestructive (causing fragmentation, breaks, release of chips, etc.); aswell as maintaining affixed the eventual fragments resulting from breaksor chips from the magnet elements 30. In the formation of the rotor, ifthere is excess of adhesive material in the axial housings 12, saidexcess is removed before cure of the adhesive material is achieved. Inthe case there is no sufficient adhesive material upon introducing themagnet elements 30 inside the axial housings 12, the latter are filledin after said magnet elements have been introduced into the axialhousings 12, before said adhesive material has cured.

The end caps 50 glued at the end of the rotor lamination are provided soas to maintain the diameter of said rotor and to guarantee the integrityof the rotor share because, since said magnet elements 30 are fragilecomponents when under traction stresses, the structure formed by themagnet elements and the resin in which they are immersed is notsufficient to assure that the centrifugal force will not cause releaseor rupture of said magnet elements 30 or even of the polar peripheralportions 20. The end caps 50 determine part of the profile of each rotorhousing for retaining a respective magnet element 30 and also act assealing means for the adhesive material deposited in said housings.

Moreover, the end caps 50 determine a uniform finish to the rotor,compensating the dimensional differences of the rotor components.

The proposed solution allows to obtain a product which has,simultaneously, the characteristics of high energetic efficiency andhigh reliability and which is adequate to be produced on a large scalewith low cost for both the product and its manufacturing process.

What is claimed is:
 1. A method for producing a rotor for an electricmotor comprising: providing a stack of a plurality of laminations of amagnetic material; forming a plurality of windows in said stack oflaminations along its axis, each window having an end portion radiallyof the rotor center, each window having an end to be at the peripheraledge of its respective lamination, there being an intermediate region ofa lamination between the ends of two of said windows that are adjacent,each lamination initially having an annular radial extension beyond whatis to be its final peripheral edge; applying an adhesive material intothe axial windows; inserting into each axial window a magnetic element;mounting an end cap to each end of the lamination stack; curing theadhesive material; removing said annular radial extension of thelaminations of the stack so that said end portion of each of saidplurality of windows is at the peripheral edges of the laminations andform a polar portion between a respective window and the peripheraledges of the laminations of the stack and an intermediate peripheralportion between two adjacent polar peripheral portions, saidintermediate peripheral portion having reduced electrical conductibilityand reduced magnetic permeability in relation to the core.
 2. Method, asin claim 1, further comprising the following steps of: depositingadhesive material on one face of an end cap to be mounted to thelamination at one end of the stack; depositing adhesive material betweenthe metallic laminations of the stack; and depositing adhesive materialbetween the lamination at the other end of the stack and another endcap.
 3. Method, as in claim 2, further comprising the following stepsof: removing the excess of the adhesive material before said materialcures; and affixing fastener elements through said polar peripheralportions of said stack of laminations and through the end caps.
 4. Amethod as in claim 1 wherein each of said windows is concave curvedfacing the peripheral edge of the lamination.